The present invention relates to a control apparatus of a motor-driven power steering (MDPS), and more particularly, to a control apparatus of an MDPS, which is capable of selectively removing booming vibrations which occur depending on a steering angle speed, thereby reducing steering vibrations.
In general, an MDPS refers to a system which uses an electric motor to provide an auxiliary torque along a direction where a driver steers a vehicle, thereby facilitating handling.
Such an MDPS automatically controls the operation of the electric motor according to a driving condition of the vehicle, unlike an existing hydraulic power steering (HPS). Thus, the MDPS may improve steering performance and steering feeling.
At this time, the MDPS determines a driving condition of the vehicle through a torque sensor to measure a driver's steering torque inputted to a steering wheel, a steering angle sensor to measure a steering angle of the steering wheel, and a vehicle speed sensor to measure vehicle speed, and provides an auxiliary torque through the electric motor according to the steering torque applied to the steering wheel by the driver.
Furthermore, the MDPS sets an auxiliary torque proportional to the steering torque, applies a proportional gain to maintain the proportional relation, and reduces or smoothes a steering force of the driver. Simultaneously, the MDPS suppresses torque ripples generated by the electric motor or vibrations such as disturbance transmitted from the ground, thereby improving the driver's feeling.
In order to suppress the torque ripples generated from the electric motor or vibrations such as ground disturbance, the MDPS uses a hybrid filter including a low pass filter (LPF) and a high pass filter (HPF), and extracts a steering component through the LPF so as to control the steering auxiliary torque. Simultaneously, the MDPS extracts high-frequency vibration components such as torque ripples through the HPF, and controls the high-frequency vibration components using a controller different from a controller for a low frequency.
Furthermore, the MDPS extracts an RPM of the electric motor or angular speed vibration component of the steering angle using a band pass filter (BPF), reduces a signal obtained by adding a gain to the vibration component from a target current, calculates a new target current, and performs negative feedback control for the angular speed, thereby reducing vibration.
As such, the vibration caused by the torque ripples are removed through the hybrid filter or BPF. However, the MDPS has a problem in that it does not properly deal with booming vibrations caused by a worm wheel depending on steering angle speed.